Hollywood heavyweights MGM and Sylvester Stallone are hoping the sixth round of the “Rocky” saga delivers a box-office knockout.

MGM sid yesterday it has signed Stallone to write a “Rocky VI” screenplay with an update to the story of the scrappy Philadelphia palooka who becomes the champion of the world.

So far, details were sketchy because Stallone – who wrote and directed 1976’s original “Rocky” – has just been hired.

But the intention is to avoid a big-budget sequel and return to the gritty feel of the original.

Early plans for “Rocky VI” has the 56-year-old Stallone portraying Rocky Balboa once more. This time, Rocky is running a youth center when – holy Larry Holmes! – he’s lured out of retirement for one last fight.

The first “Rocky” was a labor of love for Stallone. Made for a little more than $1 million, “Rocky” raked in an astounding $220 million in worldwide ticket sales. It earned critical acclaim and won the Oscar for Best Picture.

The sequels all grossed over $100 million in ticket sales – except for the final installment, “Rocky V” in 1990, which took a dive with a pathetic $40 million gross and a flurry of critical jabs from disgusted critics.